The objectives of this work are: 1) to study the roles of flow, diffusion, and blood rheology in thrombosis, particularly in arterial thrombosis where platelets are believed to play a prominent role; and 2) to determine the clinical applicability of results of such studies to two cardiovascular disorders: acute myocardial infarction, and cyanotic congenital heart disease. In the process, a determination will be made of the value of establishing a laboratory of clinical hemorhreology. Central to these studies is a chamber, recently developed, with which adenosine diphosphate (ADP)-induced platelet aggregation can be quantified in heparinized or citrated, flowing, whole blood by means of videodensitometry.